A boring machine for perforating the ground is generally based on a technique of simply circulating a bit (Oscillating method), a technique of not only circulating a bit or a ball cutter but also pressurizing the same (Reverse Circulation Drilling method: ROC), and so on.
The oscillation method can cope with a soft ground condition, that is, a boring work is properly carried out through soft ground such as soil. However, for a hard-boring operation, it is necessary to demolish rocks under the ground by dropping a large-sized hammer, requiring additional equipment such as a pile driver.
Meanwhile, in the RCD method, which is an advanced method compared to the oscillation method from the viewpoint of boring capacity, a rock bed is dug such that a soil layer is first dug using an oscillator or a rotator, both a soft rock layer and a hard rock layer are dug by rotating a specially designed bit attached to an end portion of a rod. The RCD method is still poor in boring capacity.
To overcome the foregoing disadvantages, there have been proposed a conventional boring machine constructed to strike and rotate a bit attached to an end portion of a rod during a digging work. The proposed conventional boring machine has a hammer providing a rotational force from an upper portion of the rod and providing a striking force to a lower end of the rod having the bit using air pressure or hydraulic pressure.
In the above-described boring machine, the air pressure or hydraulic pressure is necessarily supplied to the hammer installed at the lower end of the rod having the bit. Thus, as the depth of a bored hole increases, the configuration becomes relatively complicated.
In another conventional boring machine, a vibrator and a bit installed at an end of a rod installed in the vibrator are provided, and the vibrator transfers a rotational force and a striking force to the rod, thereby performing a boring work. The vibrator for applying a shock to the rod includes a device driven by the flow of one or more kinds of hydraulic fluids supplied from a hydraulic supply circuit, and a shock generated from the vibrator is transferred to the rod through a shank. The shank transfers a rotational force derived from a hydraulic motor to the rod.
EP 058,650 and EP 856,637 disclose bonding piston devices in which a hydraulic pressure is supplied from a main supply circuit of a striking device.